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<a name="boost.proto.when_Gra_1_3_32_5_52_2_1_7.impl"></a><div class="titlepage"></div>
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<h2><span class="refentrytitle">Struct template impl</span></h2>
<p>boost::proto::when&lt;Grammar, &gt;::impl</p>
</div>
<h2 class="refsynopsisdiv-title">Synopsis</h2>
<div class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link" href="../../../proto/reference.html#header.boost.proto.transform.when_hpp" title="Header &lt;boost/proto/transform/when.hpp&gt;">boost/proto/transform/when.hpp</a>&gt;

</span>
<span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> <a class="link" href="../../../Expr.html" title="Concept Expr">Expr</a><span class="special">,</span> <span class="keyword">typename</span> State<span class="special">,</span> <span class="keyword">typename</span> Data<span class="special">&gt;</span> 
<span class="keyword">struct</span> <a class="link" href="impl.html" title="Struct template impl">impl</a> <span class="special">:</span> <span class="keyword"></span> 
    <span class="identifier">boost</span><span class="special">::</span><span class="identifier">remove_reference</span><span class="special">&lt;</span> 
      <span class="keyword">typename</span> <span class="identifier">mpl</span><span class="special">::</span><span class="identifier">eval_if_c</span><span class="special">&lt;</span>
        <a class="link" href="../result_of/has_env_var.html" title="Struct template has_env_var">proto::result_of::has_env_var</a><span class="special">&lt;</span><span class="identifier">Data</span><span class="special">,</span> <a class="link" href="../transforms_type.html" title="Struct transforms_type">proto::transforms_type</a><span class="special">&gt;</span><span class="special">::</span><span class="identifier">value</span><span class="special">,</span>
        <a class="link" href="../result_of/env_var.html" title="Struct template env_var">proto::result_of::env_var</a><span class="special">&lt;</span><span class="identifier">Data</span><span class="special">,</span> <a class="link" href="../transforms_type.html" title="Struct transforms_type">proto::transforms_type</a><span class="special">&gt;</span><span class="special">,</span>
        <a class="link" href="../result_of/env_var.html" title="Struct template env_var">proto::result_of::env_var</a><span class="special">&lt;</span><span class="identifier">Data</span><span class="special">,</span> <a class="link" href="../data_type.html" title="Struct data_type">proto::data_type</a><span class="special">&gt;</span>
      <span class="special">&gt;</span><span class="special">::</span><span class="identifier">type</span>
    <span class="special">&gt;</span><span class="special">::</span><span class="identifier">type</span>
      <span class="special">::</span><span class="keyword">template</span> <span class="identifier">when</span><span class="special">&lt;</span> <span class="identifier">Grammar</span> <span class="special">&gt;</span>
        <span class="special">::</span><span class="keyword">template</span> <span class="identifier">impl</span><span class="special">&lt;</span> <span class="identifier">Expr</span><span class="special">,</span> <span class="identifier">State</span><span class="special">,</span> <span class="identifier">Data</span> <span class="special">&gt;</span>
<span class="special">{</span>
<span class="special">}</span><span class="special">;</span></pre></div>
<div class="refsect1">
<a name="id-1.3.32.5.54.10.4.5.4"></a><h2>Description</h2>
<p>
              The implementation of the <code class="computeroutput">impl</code> struct depends on whether the <code class="computeroutput">Data</code>
              parameter is a transform environment that contains a value corresponding to the
              <a class="link" href="../transforms_type.html" title="Struct transforms_type">proto::transforms_type</a> key. If so, that value is treated as a
              map from rules to transforms. Otherwise, the <code class="computeroutput">Data</code> type itself is treated
              as such a map.
            </p>
</div>
</div>
<div class="copyright-footer">Copyright © 2008 Eric Niebler<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
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